Abstract
The use of stable isotopes of hydrogen and oxygen is a tool widely used to trace water paths along the hydrological cycle, providing support for understanding climatic conditions in different spatial scales. One of the main synoptic scale events acting in southeastern Brazil is the South Atlantic Convergence Zone (SACZ), which causes a large amount of precipitation from southern Amazonia to southeastern Brazil during the southern summer. In order to determine the isotopic composition of precipitation during the action of SACZ in São Francisco Xavier in southeastern Brazil, information from the Weather Forecasting and Climate Studies Center of the National Institute for Space Research (CPTEC) was used regarding SACZ performance days, the retrograde trajectories of the HYSPLIT model, and images from the GOES-16 satellite, in addition to the non-parametric statistical tests by Spearman and Kruskal–Wallis. A high frequency of air mass trajectories from the Amazon to southeastern Brazil was observed when the SACZ was operating. During the SACZ events, the average isotopic composition of precipitation was more depleted, with a δ18O of −9.9‰ (±2.1‰), a δ2H of −69.3‰ (±17.9‰), and d-excess of 10.1‰ (±4.0‰). When disregarding the SACZ performance, the annual isotopic composition can present an enrichment of 1.0‰ for δ18O and 8.8‰ for the δ2H. The long-term monitoring of trends in the isotopic composition of precipitation during the SACZ events can assist in indicating the evapotranspiration contribution of the Amazon rainforest to the water supply of southeastern Brazil.
Highlights
Stable isotopes of hydrogen and oxygen are one of the main ecohydrological techniques for tracking water during its cycle, acting as a kind of “water fingerprint” [1]
The results of this study revealed that during the periods in which the South Atlantic Convergence Zone (SACZ) was active in the southeastern region of Brazil, in São Francisco Xavier, the isotopic signal of precipitation was more depleted (δ18 O of −9.9‰ (±2.1‰) and δ2 H of −69.3‰
The isotopic depletion of precipitation during SACZ events is explained by the Rayleigh distillation process that occurs during humidity transportation from Amazon to southeastern Brazil
Summary
Stable isotopes of hydrogen and oxygen are one of the main ecohydrological techniques for tracking water during its cycle, acting as a kind of “water fingerprint” [1]. One of the applications of the use of isotopes is to determine their composition during precipitation, with the performance of synoptic scale events, enabling the tracking of moisture that contributes to their formation [7,8,9]. This application can serve as a useful tool for validating atmospheric models [10] and for a better understanding of isotopic values in the tropical region [11]
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